Liquid crystalline thermosets from ester, ester-imide, and ester-amide oligomers

ABSTRACT

Main chain thermotropic liquid crystal esters, ester-imides, and ester-amides were prepared from AA, BB, and AB type monomeric materials and were end-capped with phenylacetylene, phenylmaleimide, or nadimide reactive end-groups. The resulting reactive end-capped liquid crystal oligomers exhibit a variety of improved and preferred physical properties. The end-capped liquid crystal oligomers are thermotropic and have, preferably, molecular weights in the range of approximately 1000-15,000 grams per mole. The end-capped liquid crystal oligomers have broad liquid crystalline melting ranges and exhibit high melt stability and very low melt viscosities at accessible temperatures. The end-capped liquid crystal oligomers are stable for up to an hour in the melt phase. These properties make the end-capped liquid crystal oligomers highly processable by a variety of melt process shape forming and blending techniques including film extrusion, fiber spinning, reactive injection molding (RIM), resin transfer molding (RTM), resin film injection (RFI), powder molding, pultrusion, injection molding, blow molding, plasma spraying and thermo-forming. Once processed and shaped, the end-capped liquid crystal oligomers were heated to further polymerize and form liquid crystalline thermosets (LCT). The fully cured products are rubbers above their glass transition temperatures. The resulting thermosets display many properties that are superior to their non-end-capped high molecular weight analogs.

This application claims the benefit of U.S. provisional application No.60/232,504, filed Sep. 13, 2000.

ORIGIN OF THE INVENTION

This invention was made by employees of the United States Government andmay be manufactured and used by or for the Government for governmentalpurposes without the payment of any royalties thereon or therefor.

1. Field of the Invention

The present invention relates generally to liquid crystalline polymersand liquid crystal thermosets. Specifically, the invention relates toliquid crystalline ester, ester-imide, and ester-amide oligomers and theimproved physical properties of such species when they are end-cappedwith phenylacetylene, phenylmaleimide, or nadimide terminatedmonofunctional reactants. The invention also relates to the ability toprocess liquid crystal polymers and their use in melt process shapeforming and blending techniques such as film extrusion, fiber spinning,reactive injection molding (RIM), resin transfer molding (RTM), resinfilm injection (RFI), powder molding, pultrusion, injection molding,blow molding, and thermo-forming.

2. Description of the Related Art

High molecular weight linear ester-based thermotropic liquid crystallinepolymers (TLCPs) are known in the literature. Non-end-capped TLCPcopolyesters are taught by Kuhfuss and Jackson in U.S. Pat. No.3,778,410 and U.S. Pat. No. 3,804,805. TLCP polyesters with non-reactivephenylester and ethylester end-cap groups, that can only be thermoset atelevated temperatures via oxidative backbone crosslinking, are taught byCalundann in U.S. Pat. No. 4,067,852 and U.S. Pat. No. 4,161,470 andCalundann et al in U.S. Pat. No. 4,083,829. McCarthy et al in U.S. Pat.No. 5, 319,064 and Plotzker et al in U.S. Pat. No. 5,688,895 teach highmolecular weight liquid crystalline poly(ester-amide)s, Alanko et alteach, in U.S. Pat. No. 5,843,541, high molecular weightpoly(ester-imide)s, and Hisgen et al teach high molecular weightpoly(ether-ester-imide)s in U.S. Pat. No. 4,762,906. The McCarthy et al,Plotzker et al, Alanko et al, and Hisgen et al patents do not teachpolymers with melt viscosities in the range of approximately 1 toapproximately 250 poise, and the claimed high molecular weight liquidcrystalline polymers have neither reactive end-caps nor rubbercharacteristics above T_(g). Kricheldorf et. al. in Mol. Cryst. Liq.Cryst., 254, 87 (1994) teach other aliphatic and aromatic liquidcrystalline poly(ester-imide)s, while Calundann et al teach otherthermotropic poly(ester-amide)s in Mol. Cryst. Liq. Cryst., 157, 615(1988) and U.S. Pat. No. 4,351,918. All of the above materials are verydifficult to melt process due to their high melt viscosities.

Improved melt processability of linear high molecular weight TLCPs wasachieved by the addition of small amounts of low molecular weightorganic compounds during the melt processing steps of the high molecularweight liquid crystal polymers by the teachings of Froix in U.S. Pat.No. 4,267,289 and Yoon in U.S. Pat. No. 4,581,399. Charbonneau et al inU.S. Pat. No. 4,746,694 teach liquid crystal polymers with relativelylow melt viscosities (200-1000 poise at 345° C. and a shear rate of 100radials/sec) by disrupting the linear progression of the polymerbackbone. This process results in undesirable volatiles.

Thermosets have been prepared from thermotropic liquid crystallinepolymers. Uryu and Kato teach, in U.S. Pat. No. 4,710,547, thermotropicliquid crystal thermosets (TLCTs) via incorporation of trifunctionalcross-link units into the TLCPs in order to immobilize the anisotropicmelt. Haider et al teach, in U.S. Pat. No. 5,216,073, a moldablecomposition by blending a liquid crystal polyester with anepoxy-functionalized rubber. In U.S. Pat. No. 4,654,412, Calundann et alteach incorporation of stilbene and tolane type difunctional monomersinto the backbone of main chain wholly aromatic liquid crystallinepolyesters in which cured shaped articles made of these polymers wereprepared by backbone crosslinking using a maleic anhydride dippingprocedure requiring an undesirable second process step.

Several patents filed by Benicewicz et al, U.S. Pat. No. 5,114,612, U.S.Pat. No. 5,198,551, U.S. Pat. No. 5,315,011, U.S. Pat. No. 5,475,133,and U.S. Pat. No. 5,575,949 and articles, A. E. Hoyt and B. C.Benicewicz, J. Polym. Sci.: Part A: Polym. Chem., 28, 3417 (1990); E. P.Douglas, D. A. Langois, B. C. Benicewicz, Chem. Mat., 6, 1925 (1994); W.Mormann, C. Kuckertz, Macromol. Chem. Phys., 199, 845 (1998), and A. J.Gavrin, C. L. Curts, E. P. Douglas, J. Polym. Sci.: Part A: Polym.Chem., 37, 4184 (1999), teach solution prepared well-defined lowmolecular weight pure ester and amide based TLCTs having self-reactiveend-cap groups such as propargyl, ethynylphenyl, maleimide, nadimide,and methyl nadimide. The Benicewicz et al literature teaches neitheroligomeric materials nor materials that are rubbers above their T_(g).The Benicewicz et al data indicates that their compounds will have largeexothermic activity during large batch productions and that theirmaterials have very short melt process windows.

Lubowitz et al teach, in U.S. Pat. Nos. 4,661,604, 4,684,714, U.S. Pat.No. 4,739,030, U.S. Pat. No. 4,851,501, and U.S. Pat. No. 5,550,204self-reactive end-cap monomers to prepare oligomeric polymer resins,including polyesters. Lubowitz et al, however, do not teach using theclaimed end-caps with liquid crystal oligomers. Lubowitz et al, further,teach the use of end-cap groups that will not survive the meltcondensation polymerization conditions. Finally, Lubowitz et al do notteach materials with melt viscosities in the range of approximately 1 toapproximately 250 poise at a shear rate of 100 radials/second.

Bilow et al teach, in U.S Pat. No. 3,864,309, polyimide oligomersend-capped with terminal acetylene or cyano groups. Bilow et al's use ofthe term “oligomer” is inconsistent with our present use of the tenri“oligomer.” Bilow et al teach low molecular weight pure end-cappedirnides as opposed to low molecular weight polyimide oligomers; theBilow et al patent teaches end-capped backbone structures of only oneunit wherein an entire sample contains only molecules of the same lengthand molecular weight. Bilow et al teach the use of end-cap groups thatwill not survive melt condensation polymerization conditions. Finally,Bilow et al teach materials that are neither liquid crystalline nor havemelt viscosities in the range of approximately 1 to approximately 250poise at a shear rate of 100 radials/second.

Reinhardt et al teach, in U.S. Pat. No. 4,513,131, phenylacetyleneend-capped low molecular weight pure aryl-ethers as opposed to thepolyester, poly(ester-amide), and poly(ester-imide) oligomers. Reinhardtet al teach materials that are not liquid crystals. Reinhardt et atteach pure low molecular weight polymer samples as opposed to theoligomeric mixtures.

Similarly, Sheppard et al in U.S. Pat. No. 4,851,495, Kwiatkowski et alin U.S. Pat. No. 3,839,287, Kovar et al in U.S. Pat. No. 3,975,444,Baudouin et al in U.S. Pat. No. 4,225,497, and Kumar et al in U.S. Pat.No. 4,550,177 teach materials that are not liquid crystalline. Thesepatents also do neither teach materials with melt viscosities in therange of approximately 1 to approximately 250 poise at a shear rate of100 radials/second nor do they teach the use of end-cap groups that willsurvive melt condensation polymerization conditions.

The claimed invention of reactive end-capped oligomeric liquidcrystalline polyesters, poly(ester-amide)s, and poly(ester-imide) isnovel and non-obvious over the prior art. The present invention wasprepared via melt condensation techniques as opposed to solutionchemistry and produced oligomeric mixtures as opposed to well definedpure molecular species. The present invention is oligomeric rather thanpure in that they contain a mixture of varying higher weight and/orlength TLCPs, relative to the pure analogs, and generally have molecularweight distributions of approximately of 1000 to approximately 15,000grams per mole. Linking of individual oligomers in the present inventionprimarily occurs via reactions only between the end-cap groups ratherthan backbone to backbone or backbone to end-cap group crosslinking.Finally, the present invention has unexpected and improved physical andmelt processing characteristics including melt viscosities in the rangeof approximately 1 to approximately 250 poise at a shear rate of 100radials/second, rubber behavior above the T_(g), exhibit no exothermiicbehavior during batch production, and have melt process windows of up toan hour at approximately 300° C.

SUMMARY OF THE INVENTION

Based on what has been stated above, it is an objective of the presentinvention to prepare high performance end-capped liquid crystal ester,ester-imide, and ester-amide oligomers. These end-capped liquid crystaloligomers were prepared via melt condensation techniques over a widetemperature range while maintaining the liquid crystal state andproperties. The end-capped liquid crystal oligomers have greatly reducedmelt flow viscosities over extended periods of time, relative to otherhigher molecular weight analogs, allowing for melt processing. Theend-cap groups were chosen to be stable in the temperature range usedfor the melt condensation preparation of the liquid crystal oligomers.The end-cap groups were chosen to polymerize with each other attemperatures above the range used for the melt condensation preparationof the oligomers and above that temperature which will inducechain-extension of the liquid crystal oligomers. The melt processedend-capped liquid crystal oligomers were converted into to liquidcrystal thermosets by exposure to temperatures sufficiently high tocause end-cap polymerization while not inducing cross-linking of theliquid crystal backbone. The degree of end-cap polymerization wascontrolled through varying length and temperature of exposure.

It is another objective of the present invention to prepare highperformance end-capped liquid crystal ester, ester-imide, andester-amide oligomers that can be prepared using commercially availablemonomers in a relatively inexpensive and environmentally benign onevessel synthesis.

It is another objective of the present invention to prepare highperformance end-capped liquid crystal ester, ester-imide, andester-amide oligomers that are amenable to melt process shape formingand blending techniques such as film extrusion, fiber spinning, reactiveinjection molding (RIM), resin transfer molding (RTM), resin filminjection (RFI), powder molding, pultrusion, injection molding, blowmolding, plasma spraying, and thermo forming. More specifically, theobjective is to prepare high performance end-capped liquid crystalester, ester-imide, and ester-amide oligomers that are suitable forResin Transfer Molding (RTM). The preferred oligomers have low meltviscosities, low dielectric constants, low moisture absorption, highsolvent resistivity, and high adhesion and barrier properties. Mostspecifically, the oligomers have the above qualities and are able to beused as composite matrices, adhesives, high barrier coatings, lowdielectric films, membranes, fibers, and moldings.

The “backbones” of the end-capped liquid crystalline ester, ester-imide,or ester-amide oligomers were prepared from the reaction between varyingquantities and combinations of one or more aromatic, heterocyclic oraliphatic dicarboxylic acids, aromatic, heterocyclic or aliphatic diolsaromatic, heterocyclic or aliphatic diamines, hydroxybenzoic acids andaminobenzoic acids. The preferred embodiments of the end-capped ester,ester-imide, and ester-amide oligomers backbones are depicted in FIG. 1,wherein R is the structural units depicted in FIG. 2 and Ar is thestructural units depicted in FIG. 3 and X is the structural unitsdepicted in FIG. 4. The “backbone” liquid crystal oligomers aresimultaneously end-cap terminated with stoichiometric quantities ofmono-functional reactants to control oligomer chain length. The end-capunits for the end-capped ester, ester-imide, and ester-amide oligomerscan be prepared by methods in the art and include phenylacetylenederivatives of general formula (I)

and/or phenylmaleimide of general formula (II),

and/or nadimide of general formula (III)

wherein Y can be a carboxy, hydroxy, amino group or any reactive analogthereof (e.g., acetoxy, propionoxy, butoxy, etc.), or an esterifiedcarboxy group (e.g., methylbenzoate, ethylbenzoate, phenylbenzoate,etc.). The R′ substituents can be identical or different on any givenend-cap unit provided they do not interfere with the melt condensationsynthesis of the liquid crystal oligomers or the higher temperaturecuring step. Possible R′ substituents include hydrogen, lower alkylgroups (preferably containing four or less carbon atoms) such as methyl,ethyl, propyl, and butryl groups, aryl groups (preferably containing sixto ten carbon atoms) such as phenyl or naphthyl groups, lower alkoxygroups such as methoxy, ethoxy, and propoxy, lower aryloxy groups suchas phenoxy or benzloxy, or halogen groups (i.e fluoro, chloro, bromo, oriodo groups). Other phenylacetylene end-cap derivatives include4-phenylethynyl-phenol and 4-phenylethynylbenzoic acid.

The present invention end-capped liquid crystal ester, ester-imide, andester-amide oligomers can be modified by means of conventionaladditives, used in conventional amounts, of stabilizers, oxidationinhibitors, agents against thermal and ultraviolet light decomposition,lubricants, mold release agents, colorants such as dyes and pigments,fibrous or pulverulent fillers and reinforcing agents, nucleatingagents, and/or plasticizers.

BRIEF DESCRIPTIONS OF THE FIGURES

FIG. 1 indicates, but does not intend to limit, the structural repeatunits of the end-capped liquid crystal ester, ester-imide, andester-amide oligomers.

FIG. 2 indicates, but does not intend to limit, the R units of thestructural repeat units of the end-capped liquid crystal ester,ester-imide, and ester-amide oligomers depicted in FIG. 1.

FIG. 3 indicates, but does not intend to limit, the Ar units of thestructural repeat units of the end-capped liquid crystal ester,ester-imide, and ester-amide oligomers depicted in FIG. 1.

FIG. 4 indicates, but does not intend to limit, the X units depicted inFIG. 3.

FIG. 5 is a sample reaction.

FIG. 6 is a sample reaction.

FIG. 7 is a sample reaction.

FIG. 8 is a composite laminate lay-up configuration of the end-cappedliquid crystal oligomers.

FIG. 9 is schematic of the cure cycle for the melt processing of6HBA/4HNA-5PE into laminate graphite cloth ((6HBA/4HNA-5PE)/IM-7).

FIG. 10 is a schematic for the cure cycle for the melt processing of6HBA/4HNA-9PE into a neat resin plaque ((6HBA/4HNA-9PE).

FIG. 11 is the mold configuration for the fabrication of a(6HBA/4HNA-9PE) plaque.

DETAILED DESCRIPTION OF THE INVENTION

Within the scope of the present invention, the term “oligomer(s)” and“oligomer mixture(s)” designate mixtures of varying backbone lengthliquid crystal polymers, of maximally 500 repeat units, within theweight range of approximately 1000 to approximately 15,000 grams permole that are not isolated as discreet molecular weight polymers.

The term “pure” designates liquid crystal compounds in which allmolecules of a given sample are of the same length and molecular weight.The terms “high weight” and “high molecular weight” designate polymersand mixtures of polymers in which additional increases in polymer lengthand weight have no effect on the physical properties, includingprocessability, of the polymers and mixtures.

Linear liquid crystal polymers (LCPs) exhibit higher degrees ofmolecular order while in the molten state than other polymeric species.The ability of these species to maintain molecular order in the moltenstate has pronounced effects on the solid state physical properties ofthis class of polymers. Specifically, liquid crystalline polymersexhibit molecular order in the solid state and lower melt viscosities athigher molecular weights. The improved molecular order in the solidstate makes liquid crystal polymers desirable for uses in shape moldedcomposite materials. Despite LCPs exhibiting reduced melt viscosities,the melt viscosities have not until now been sufficiently low to makehigher weight LCPs amenable to improved melt process shape forming andblending techniques such as film extrusion, fiber spinning, reactiveinjection molding (RIM), resin transfer molding (RTM), resin filminjection (RFI), powder molding, pultrusion, injection molding, blowmolding, plasma spraying, and thermo-forming.

Linear thermotropic liquid crystals typically have very high meltingpoints and molecular weights that limit their ability to be meltprocessed. Once formed, however, the polymers typically have very highmelting points and molecular weights that limit their ability to be meltprocessed. The present invention involves the preparation of liquidcrystal oligomers of relatively moderate weight and length viatraditional melt state condensation techniques. The liquid crystaloligomers were end-capped in the melt state with phenylacetylene,phenylmaleimide, or nadimide terminated monofunctional reactants. Theseend-caps are stable in the melt state condensation conditions needed forpreparing the liquid crystal oligomers. The end-caps were chosen so asto polymerize with each other at temperatures above the range used forthe melt condensation preparation of the oligomers but below that whichwill induce cross-linking of the liquid crystal backbone.

The resulting end-capped LCTs display many superior and improvedproperties to their non-end-capped high molecular weight analogs thatare non-obvious and unanticipated in the literature. Among theseproperties are: unusually lowered melt viscosities for these weightpolymer species compared to non-end-capped higher molecular weightanalogs and comparable and/or superior to previously end-capped lowerweight non-oligomeric species (end-capped single pure molecules),stability of melt viscosities at elevated temperatures for extendedperiods of time relative to previous liquid crystalline products, andreduced brittleness (i.e. rubber behavior) above the glass transitiontemperature.

The end-capped liquid crystal oligomers exhibit lower melt viscositiesthan the corresponding non-end-capped high weight analogs. Beingpolymeric, the end-capped liquid crystal oligomers exhibit superiorphysical properties relative to well-defined end-capped low weight pureliquid crystal esters. This class of end-capped liquid crystaloligomers, therefore, exhibits improved melt processability relative tohigher weight analogs while maintaining the benefits of being polymericrelative to well-defined end-capped low weight pure liquid crystalesters. In many instances, the lowered melt viscosity can be maintainedfor extended periods of time relative to the non-end-capped higherweight analogs and comparable and/or superior to the end-capped lowweight pure liquid crystal esters. Lowered melt viscosities make thisnew class of liquid crystal polymers more amenable to melt processing.For the first time, higher weight liquid crystal oligomers can be usedeffectively in melt process shape forming and blending techniques.

Once melt processed and shaped, the end-capped liquid crystal oligomerswere cured at elevated temperatures (temperatures above that used forthe melt state condensation) resulting in liquid crystal thermosets.This second step causes the end-caps to react with one another andfurther increases the molecular weight of the liquid crystal polymers.Traditionally, heat curing of polymer molds is carried out attemperatures sufficiently high to induce cross-linking of the polymerbackbone. Cross-linking of the backbone, however, often makes the curedproduct brittle. In the present invention, the reactions between theend-caps can be carried out at temperatures below that which wouldinduce significant cross-linking within the liquid crystal oligomerbackbone while the degree of end-cap polymerization can be controlledthrough varying length and temperature of exposure. Unexpectedly, thelack of significant backbone cross-linking produces liquid crystallinepolymers that behave as rubbers when elevated above their glasstransition temperatures rather than becoming brittle.

Method of Preparation

The “backbones” of the end-capped liquid crystalline ester, ester-imide,or ester-amide oligomers were prepared from the reaction between varyingquantities and combinations of one or more aromatic, heterocyclic oraliphatic dicarboxylic acids, aromatic, heterocyclic or aliphatic diolsaromatic, heterocyclic or aliphatic diamines, hydroxybenzoic acids andaminobenzoic acids. The preferred embodiments of the end-capped ester,ester-imide, and ester-amide oligomers backbones are depicted in FIG. 1wherein R is the structural units depicted in FIG. 2 and Ar is thestructural units depicted in FIG. 3 and X is the structural unitsdepicted in FIG. 4. The preferred general methods of preparation of theend-capped ester, ester-imide, and ester-amide oligomers are presentedin FIGS. 5, 6, and 7 wherein R₁, R₂, and R₃ can be identical ordifferent and are the structural units depicted in FIG. 2 and Ar₁, Ar₂,and Ar₃can be identical or different and are the structural unitsdepicted in FIG. 3 and X is the structural units depicted in FIG. 4. E-Yrepresents end-cap units I, II, and/or III that can be prepared bymethods available in the literature, wherein Y can be a carboxy,hydroxy, amino group or any reactive analog thereof (e.g., acetoxy,propionoxy, butoxy, etc.), or an esterified carboxy group (e.g.,methylbenzoate, ethylbenzoate, phenylbenzoate, etc.) and the R′substituents can be identical or different on any given end-cap unitprovided they do not interfere with the melt condensation synthesis ofthe liquid crystal oligomers or the higher temperature curing step.Possible R′ substituents include hydrogen, lower alkyl groups(preferably containing four or less carbon atoms) such as methyl, ethyl,propyl, and butryl groups, aryl groups (preferably containing six to tencarbon atoms) such as phenyl or naphthyl groups, lower alkoxy groupssuch as methoxy, ethoxy, and propoxy, lower aryloxy groups such asphenoxy or benzloxy, or halogen groups (i.e fluoro, chloro, bromo, oriodo groups). The stoichiometric amounts of each reactant and end-capgroup can be varied to prepare oligomers of varying size, weight,characteristic and chemical content. The reactions depicted in FIGS. 5,6, and 7 are generally performed at between approximately 140° C. toapproximately 350° C. The melt viscosities of the end-capped ester,ester-imide, and ester-amide oligomers are lower than theirnon-end-capped analogs.

The present invention end-capped liquid crystal ester, ester-imide, andester-amide oligomers can be modified by means of conventionaladditives, used in conventional amounts, of stabilizers, oxidationinhibitors, agents against thermal and ultraviolet light decomposition,lubricants, mold release agents, colorants such as dyes and pigments,fibrous or pulverulent fillers and reinforcing agents, nucleatingagents, or plasticizers.

The following specific examples are provided for illustrative purposes.These examples do not serve to limit the scope of the invention.

EXAMPLES Preparation of Reactive End-Caps

The following examples illustrate the reaction sequence for thesynthesis of the reactive end groups that were used for the preparationof end-capped ester, ester-imide, and ester-amide oligomers.

Example A Phenylacetylene Terminated Carboxylic Acid; PE-COOH

Into a 250 mL two-neck round bottom flask equipped with a mechanicalstirrer, condenser and a nitrogen gas inlet was placed 4-aminobenzoicacid (8.0 g, 58 mmol), 4phenylethynylphthalic-anhydride (14.5 g, 58mmol) and 150 mL glacial acetic acid. This mixture was stirred at 25° C.for 1 hour after which the temperature was raised to reflux for 12hours. The reaction mixture was cooled to 25° C. and the precipitatedproduct was collected by filtration, washed twice with hot ethanol anddried under vacuum at 100° C. for 8 hours.

Example B Phenylacetylene Terminated Acetoxy Phenol; PE-OAc

Into a 250 mL two-neck round bottom flask equipped with a mechanicalstirrer, condenser and a nitrogen gas inlet was placed 4-aminophenol(6.3 g, 58 mmol), 4-phenylethynylphthalicanhydride (14.5 g, 58 mmol) and200 mL glacial acetic acid. This mixture was stirred at 25° C. for 1hour after which the temperature was raised to reflux for 12 hours. Thereaction mixture was cooled to 25° C. and the precipitated product wascollected by filtration, washed twice with ethanol and dried undervacuum at 50° C. for 8 hours.

The dried end-cap products were refluxed in 150 mL acetic anhydride for5 hours. Yellow crystals precipitated upon cooling and were collected byfiltration, washed with ethanol and dried under vacuum at 80° C. for 8hours.

Other end groups were made using similar procedures. The yields andthermal analysis results (differential scanning calorimetry) of allcompounds are summarized in Table 1.

TABLE 1 Yields and thermal properties of the reactive end cappers. YieldTm ΔH_(fus) Exotherm ΔH_(exo) Molecular Structure Name (%) (° C.)(KJ.mol⁻¹) range (° C.) (KJ.mol⁻¹)

PE—COOH 92 347.8 36.21 363-421 −67

PE—OAc 93 236.6 38.71 340-426 −115 

PM—COOH 92 261.2 30.2 311-407 −23

PM—OAc 94 155.6 29.3 302-421 −54

NOR—COOH 77 233.1 30.61 290-360 −21

NOR—OAc 90 191.4 27.2 310-388 −32

Preparation of End-Capped Liquid Crystal Oligomers Example 1

A 100 mL 3-neck round bottom flask was charged with 4-acetoxybenzoicacid (45.1 g, 0.25 mol), 6-acetoxy-2-naphtoic acid (38.4 g, 0.17 mol),PE-COOH (2.43 g, 6.6 mmol), PE-OAc (2.52 g, 6.6 mmol) and 4 mg potassiumacetate. The flask was equipped with a sealed glass paddle stirrer, anitrogen inlet tube and an insulated distillation head. The flask waspurged with nitrogen gas, and the reaction mixture was heated over a 3hour period on a woods metal bath, under a slow stream of nitrogen, withthe reaction temperature being increased from 150° C. to 300° C. At thispoint the temperature was increased to 310° C. over 30 minutes and avacuum was slowly applied for 25 min. The opaque melt was cooled to roomtemperature and the product (6HBA/4HNA-9PE) was broken from the flaskand ground into a fine powder.

Example II

A 100 mL 3-neck round bottom flask was charged with 4-hydroxybenzoicacid (20.72 g, 0.15 mol), 6-hydroxy-2-naphtoic acid (18.82 g, 0.1 mol),NOR-COOH (1.13 g, 4 mmol), NOR-OAc (1.19 g, 4 mmol), acetic anhydride(28.1 g, 0.275 mol), and 5 mg potassium acetate. The flask was equippedwith a sealed glass paddle stirrer, a nitrogen inlet tube and aninsulated distillation head. The flask was purged with nitrogen gas, andthe reaction mixture was heated over a 1 hour period on a woods metalbath, under a slow stream of nitrogen, to 140° C. and held for 1 hour atthis temperature. The reaction temperature was increased to 250° C. in100 min. and hold at this temperature for 50 min. The reactiontemperature was increased from 250° C. to 275° C. in 30 min. and avacuum was slowly applied for 20 min. The opaque melt was cooled to roomtemperature and the product (6HBA/4HNA-9NOR) was broken from the flaskand ground into a fine powder.

Example III

A 100 mL 3-neck round bottom flask was charged with 4-hydroxybenzoicacid (20.72 g, 0.15 mol), 6-hydroxy-2-naphtoic acid (18.82 g, 0.1 mol),PM-COOH (1.17 g, 4 mmol), PM-OAc (1.23 g, 4 mmol), acetic anhydride(28.1 g, 0.275 mol), and 5 mg potassium acetate. The flask was equippedwith a sealed glass paddle stirrer, a nitrogen inlet tube and aninsulated distillation head. The flask was purged with nitrogen gas, andthe reaction mixture was heated over a 1 hour period on a woods metalbath, under a slow stream of nitrogen to 140° C. and held for 1 hour atthis temperature. The reaction temperature was increased to 250° C. in110 min. and hold at this temperature for 50 min. The reactiontemperature was increased from 250° C. to 300° C. in 30 min. and avacuum was slowly applied for 20 min. The opaque melt was cooled to roomtemperature and the product (6HBA/4HNA-9PM) was broken from the flaskand ground into a fine powder.

Example IV

A 100 mL 3-neck round bottom flask was charged with 4-acetoxybenzoicacid (19.8 g, 0.11 mol), 6-acetoxy-2-naphtoic acid (2.3 g, 0.01 mol),2,6-diacetoxynaphthalene (9.77 g, 0.04 mol), terephthalic acid (6.65 g,0.04 mol), PE-COOH (1.17 g, 3.2 mmol), PE-OAc (2.21 g, 3.2 mmol) and 4mg potassium acetate. The flask was equipped with a sealed glass paddlestirrer, a nitrogen inlet tube and an insulated distillation head. Theflask was purged with nitrogen gas, and the reaction mixture was heatedover a 3 hour period on a woods metal bath, under a slow stream ofnitrogen, with the reaction temperature being increased from 150° C. to300° C. After three hours, vacuum was slowly applied for 25 min. Theopaque melt was cooled to room temperature and the product(55HBA/20TA/5HNA/20ND-9PE) was broken from the flask and ground into afine powder.

Example V

A 100 mL 3-neck round bottom flask was charged with terephthalic acid(8.31 g, 0.05 mol), ethylene bis(4-hydroxybenzoate) (13.33 g, 0.044mol), 4-acetoxyphenylethynyl (2.77 g, 0.012 mol), and 4 mg potassiumacetate. The flask was equipped with a sealed glass paddle stirrer, anitrogen inlet tube and an insulated distillation head. The flask waspurged with nitrogen gas, and the reaction mixture was heated over a 3hour period on a woods metal bath, under a slow stream of nitrogen, withthe reaction temperature being increased from 150° C. to 260° C. Afterthree hours the temperature was increased to 280° C. over 30 minutes anda vacuum was slowly applied for 15 min. The opaque melt was cooled toroom temperature and the product (50TA/25HBA/25EG-5APE) was broken fromthe flask and ground into a fine powder.

Example VI

A 100 mL 3-neck round bottom flask was charged with 6-acetoxy-2-naphtoicacid (11.51 g, 0.05 mol), terephthalic acid (2.77 g, 0.017 mol),4-acetoxyacetanilide (3.22 g, 0.017 mol), PE-COOH (0.49 g, 1.3 mmol),PE-OAc (0.5 g, 1.3 mmol) and 3 mg potassium acetate. The flask wasequipped with a sealed glass paddle stirrer, a nitrogen inlet tube andan insulated distillation head. The flask was purged with nitrogen gas,and the reaction mixture was heated over a 3 hour period on a woodsmetal bath, under a slow stream of nitrogen, with the reactiontemperature being increased from 150° C. to 300° C. After three hours avacuum was slowly applied for 25 min. The opaque melt was cooled to roomtemperature and the product (6HNA/2TA/2AP-9PE) was broken from the flaskand ground into a fine powder.

Example VII

A 100 mL 3-neck round bottom flask was charged with terephthalic acid(7.62 g, 0.046 mol), ethylene bis(4-acetoxyanilide) (18.85 g, 0.049mol), PE-COOH (2.32 g, 6.3 mmol), and 4 mg potassium acetate. The flaskwas equipped with a sealed glass paddle stirrer, a nitrogen inlet tubeand an insulated distillation head. The flask was purged with nitrogengas, and the reaction mixture was heated over a 3 hour period on a woodsmetal bath, under a slow stream of nitrogen, with the reactiontemperature being increased from 150° C. to 300° C. At this point thetemperature was increased to 310° C. over 30 minutes and a vacuum wasslowly applied for 15 min. The opaque melt solidified and was cooled toroom temperature. The product (50TA/25AB/25EG-9PE) was broken from theflask and ground into a fine powder.

Example VIII

A 100 mL 3-neck round bottom flask was charged with 4-acetoxybenzoicacid (10.81 g, 0.06 mol), N-(3′-acetoxyphenyl)trimellitimide (11.33 g,0.4 mol), PE-COOH (0.58 g, 1.6 mmol), PE-OAc (0.61 g, 1.6 mmol) and 2 mgpotassium acetate. The flask was equipped with a sealed glass paddlestirrer, a nitrogen inlet tube and an insulated distillation head. Theflask was purged with nitrogen gas, and the reaction mixture was heatedover an 3 hour period on a woods metal bath, under a slow stream ofnitrogen, with the reaction temperature being increased from 150° C. to300° C. At this point the temperature was increased to 310° C. and avacuum was slowly applied for 20 min. The opaque melt was cooled to roomtemperature and the product (6HBA/4IM-9PE) was broken from the flask andground into a fine powder.

Characterization of End-Capped Liquid Crystal Oligomers

The end-capped liquid crystal oligomers were characterized using meltrheology, thermogravimetric analysis (TGA) and differential scanningcalormetry (DSC). All results are summarized in Tables 2 and 3.

TABLE 2 Optical microscopy and melt rheology results. Phase type (η(P)at Phase after 1 h. 100 rad.s⁻¹)/ Behavior hold at T (° C.) Example Nameat 250° C. 370° C. for 1 h. 6HBA/4HNA N N (1E5-9E5)/250 6HBA/4HNA- N N(200-900)/250 1PE 6HBA/4HNA- N N (30-9)/250 5PE I 6HBA/4HNA- N N(30-3)/250 9PE 6HBA/4HNA- N N (4E4-1E5)/250 13PE II 6HBA/4HNA- N N(5E3-1E4)/250 9NOR III 6HBA/4HNA- N N — 9PM IV 55HBA/20TA/ N N (150)/250(2)/280 5HNA/20N D-9PE V 50TA/25HBA/ N I (2)/250 25EG-5APE VI6HNA/2TA/2AP- N N (30)/250 (9)/280 9PE VII 50TA/25AB/ N N — 25EG-9PEVIII 6HBA/4IM-9PE N N — N = nematic I = isotropic

TABLE 3 Thermal properties of the LC oligomers. 5% wt. loss 5% wt. in N₂loss in air Tg (° C.) Tm (° C.) Tg (° C.) Tm (° C.) Example Name (° C.)(° C.) Heat 1 Heat 1 Heat 2 Heat 2 6HBA/4HNA 414 401 91 — 91 —6HBA/4HNA-1PE 431 411 100  205 — — 6HBA/4HNA-5PE 458 454 85 — — — I6HBA/4HNA-9PE 454 449 80 — 84 — 6HBA/4HNA-13PE 409 393 — 245 — — II6HBA/4HNA- 433 401 — — — — 9NOR III 6HBA/4HNA-9PM 394 361 — — — — IV55HBA/20TA/5H 438 400 — — 231  — NA/20ND-9PE V 50TA/25HBA/25E 368 333 56185 65 — G-5APE VI 6HNA/2TA/2AP- 427 400 — — 139  — 9PE VII50TA/25AB/25EG- 9PE VII 6HBA/4IM-9PE 385 408 138  317 210  294 Note: Theheating rate for TGA experiments was 2.5° C. min⁻¹ and a heating rate of10° C. min⁻¹ was used for the DSC experiments. The TGA samples werecured at 350° C. for 1 h. prior to the measurement. The DSC samples wereheated to 350° C. and hold for 1 h. prior to the second heat.

Melt Processing Examples of End-Capped Liquid Crystal Oligomers

Thin films were prepared by heating 7HBA/3HNA 9PE, heated with 10°C./min. to 370° C. and were held at this temperature for 1 hour to allowthe reactive end groups to react. The norbomene and phenylmaleimide endgroups react at temperatures between 250° C. and 400° C. Thephenylacetylene end groups are more stable in the melt and nosignificant end group chemistry could be observed below 310° C., i.e. noincrease in melt viscosity could be observed. With exception of theester oligomers with aliphatic spacers, all oligomers formed films thatdid not flow under stress and appeared nematic in nature after curing.Films that have a low concentration of reactive end groups behave moreelastic above their T_(g), while the films with high concentrations ofreactive end groups are more brittle in nature. Isotropizationtemperatures could not be observed for the wholly aromatic oligomerseries. Mechanical test data are shown in Tables 4 and 5.

TABLE 4 Film tensile test results at room temperature Strain ModulusYield stress 7HBA/3HNA-9PE at break (%) (GPa) (MPa) mean 2.635 2.70055.187 Std. dev. 0.088 0.144  2.760

TABLE 5 Film 3-point bending test results (ASTM D790) at roomtemperature Strain Modulus Max stress 7HBA/3HNA-9PE at peak (%) (GPa)(MPa) mean 3.215 3.925 91.5 Std. dev. 0.757 0.409 10.0

Example IX Composite Laminate Film

One ply of kapton film was placed on a metal plate and 25 grams of(6HBA/4HNA-5PE) was spread evenly on top of the kapton film. Four pliesof plain weave IM-7 graphite cloth was placed above the powder, followedby two plies of 0.0025″ Teflon bleeder/breather cloth. FIG. 8 is acomposite laminate lay-up configuration of the end-capped liquid crystaloligomers. The entire lay-up was contained in a metal dam and was vacuumbagged utilizing a standard vacuum bagging process for high temperaturepolyimides. The (6HBA/4HNA-5PE)/IM-7 cloth was heated to 482° F. with 5″Hg of vacuum and held for one hour. During the hour hold, the viscosityof the resin decreased and was forced up through the plain weave clothvia the 5″ Hg of vacuum. After 60 minutes at 482° F., the vacuum wasincreased to 20″ Hg and the temperature was ramped to the final curetemperature of 700° F. As the temperature reached 600° F., full vacuumwas applied (30″ Hg) to allow increased consolidation pressure and toensure resin infusion into the IM-7 fibers. When the final holdtemperature was reached (700° F.) the part was held for 30 minutes toallow the reactive end groups (PE) to react and then the laminate wascooled to ambient temperature while maintaining full vacuum. At ambienttemperature, the mold was removed from the vacuum bag and the laminatewas removed from the metal dam. FIG. 9 is schematic of the cure cyclefor the melt processing of 6HBA/4HNA-5PE into laminate graphite cloth((6HBA/4HNA-5PE)/IM-7). Upon visual and ultrasonic examination, thelaminate was determined to be of good quality. This result indicatesthat the low zero shear melt-viscosity of the thermotropic LC precursorsleads to excellent wet-out of the carbon fiber reinforcement.

Example X Resin Plaque

(6HBA/4HNA-9PE) was fabricated into a neat resin plaque by the processshown in FIG. 10. The neat resin plaques were fabricated in order totest mechanical properties such as; K1C (opening mode fracturetoughness), flexure strength and modulus, and compressive strength andmodulus. A conceptual drawing of the mold that was used to fabricate theneat resin plaques is depicted in FIG. 11. The mold was 3.5″×3.5″ andwas restricted to a maximum height of 0.5″. The height was restricted byplacing steel spacers in the mold to ensure the final dimensions of theplaque were at least 3″×3″×0.5″. Two steel spacers with dimension,1.5″×0.25″×0.5″, were placed in the mold. A piece of Kapton film wasplaced into the base of the mold and onto the film was poured 100 gramsof (6HBA/4HNA-9PE). This material was compacted in a hydraulic press andanother piece of Kapton film and the steel plunger were inserted intothe mold. The entire mold was placed in a vacuum hydraulic press. The(6HBA/4HNA-9PE) was heated to 572° F. with no pressure or vacuum andheld for 30 min. During this hold, the (6HBA/4HNA-9PE) began to reactwhich was evident by a increase in viscosity and the production ofacetic acid. After 30 min. at 572° F., the temperature was increased to608° F. and 30″ Hg of vacuum was applied. The polymer was held at 608°F. for 30 min. and the temperature was increased to its final holdingtemperature of 675° F. As the temperature approached 675° F., pressure(100 psi) was applied. The plaque was held at 675° F. for 1 hour and wascooled to room temperature under full vacuum and pressure. The plaquewas removed from the mold and visual inspection indicated a wellconsolidated neat resin plaque with a density of 0.86 g/cm³.

Example XI Foam Structure

A foamed structure was fabricated by using (6HBA/4HNA-9PE) that was notfully polymerized. The process was the same as described in Example X.During the high temperature vacuum step the released acetic acid acts asa blowing agent and a plaque was obtained that has a well defined porousdensity (0.43 g/cm³) and shows good mechanical properties.

Example XII Adhesive Resin

To test adhesive bonding, an adhesive scrim cloth was saturated withmolten (6HBA/4HNA-9PE) at 280° C. The resulting cloth contained 28 wt %resin and was placed between two titanium coupons to form a lap jointwith a surface area of 2.54×1.27 cm (1×0.5 inch). The titanium couponswere sand blasted, treated with Pasa-Gel 107, washed, and dried prior touse. The lap joints were bonded in a heated press for 1 h. at 350° C.and 15 psi. The resulting bonded lap joints were tested at roomtemperature according to ASTM D 1002. The results are summarized inTable 6.

TABLE 6 Shear strength of (6HBA/4HNA-9PE) on titanium (Ti, 6A1-4V) atroom temperature. Area Bond of Length of Press Bondline overlap overlapShear Sample Set MPa (psi) μm (mils) (inch²) (inch) Str. (psi) 1 0.1(15) 28 (1.1) 0.5 0.5 1998 2 0.1 (15) 20 (0.8) 0.5 0.5 1863

1. An oligomer mixture with self-reactive end-caps comprising thegeneral structure

wherein E and E′ are

Z is

wherein Ar is


2. An oligomer mixture with self-reactive end-caps comprising thegeneral structure

wherein E and E′ are

Z is

wherein Ar₁ and Ar₂ are


3. An oligomer mixture with self-reactive end-caps comprising thegeneral structure

wherein E and E′ are

and Z is selected from the group consisting of

where Ar₁ and Ar₃ are

and Ar₂ is